Add support for .srcjar files from genrules and srcs

Allow srcs to contain .srcjar files, which will be extracted just
before javac.  Also allow genrules and generated sources to directly
return .srcjar files.

Test: m checkbuild
Change-Id: Ie4cf60ecb9d2ec63a4c2275221544203b1383597

scripts/extract-srcjars.sh

@@ -0,0 +1,30 @@
+#!/bin/bash -e
+
+# Extracts .java files from source jars in a specified directory and writes out a list of the files
+
+if [ -z "$1" -o -z "$2" ]; then
+  echo "usage: $0 <output dir> <output file> [<jar> ...]" >&2
+  exit 1
+fi
+
+output_dir=$1
+shift
+output_file=$1
+shift
+
+rm -f $output_file
+touch $output_file
+
+for j in "$@"; do
+  for f in $(zipinfo -1 $j '*.java'); do
+    echo $output_dir/$f >> $output_file
+  done
+  unzip -qn -d $output_dir $j '*.java'
+done
+
+duplicates=$(cat $output_file | sort | uniq -d | uniq)
+if [ -n "$duplicates" ]; then
+  echo Duplicate source files:
+  echo $duplicates
+  exit 1
+fi